USB: serial: add zte_ev.c driver

This adds a driver for the zte_ev set of usb to serial devices.  It is
based on a patch floating around the internet that modified the generic
usb-serial driver to only work for this type of device.

I've left comments in the code that I think show the data commands being
sent to the device, which I'm guessing come from a usb analyzer.  Maybe
they can help others out as well.

Many thanks to nirinA raseliarison for pointing the original patch out
to me, and for testing that the driver works properly.

Tested-by: nirinA raseliarison <nirina.raseliarison@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>